In recent years, research on an ad hoc network is being progressed in which a plurality of communication devices (hereinafter, referred to as node devices) are autonomously and distributively connected with each other (see, for example, Japanese Laid-open Patent Publication No. 2006-191218). Each node device of the ad hoc network independently constructs a network according to communication environment.
Specifically, in the ad hoc network, an access point is not installed and each node device relays a data frame received from a node device adjacent thereto (hereinafter, referred to as an adjacent node device) to other adjacent node device based on a network topology to transmit the data frame to a destination node device. In this case, each node device selects a path having a better transmission quality to transmit the data frame.
Since the network environment varies at the moment instantly, the data frame is not always transmitted to the destination node device even when each node device has transmitted the data frame based on the network topology.
For example, the data frame transmitted to the adjacent node device may be looped back. In this case, a node device which transmitted the data frame (here, the node device is referred to as a relay node device) determines that a path via the adjacent node device selected as the transmission destination is not a normal path and changes the path. Also, the relay node device retransmits the data frame which is looped back (hereinafter, referred to as the loop data) to other adjacent node device.
Further, a fraudulent node device which interferes the relaying of a frame such as a data frame also exists in the network environment. It is assumed that such a fraudulent node device fraudulently receives the data frame transmitted to the adjacent node device by, for example, the relay node device and transmits the fraudulently received data frame (hereinafter, referred to as a redundant data) to the relay node device. In this case, the relay node device erroneously determines that the data frame transmitted to the adjacent node device is looped back and changes the path based on the erroneous determination even though the path is normal.